1. Field of the Invention
This invention relates to driving the cathodes of hot cathode gas discharge lamps and, in one embodiment, also to driving the arc.
2. Description of the Related Art
Hot cathode gas discharge lamps, particularly the fluorescent lamp variety, are widely used in displays and in interior lighting. Voltage drive circuitry is commonly used to drive the cathodes causing the filaments to heat and thus release enough electrons into the envelope for the lamp to arc from the voltage applied across opposing cathodes. For some applications, especially those in which a lamp is turned on and off thousands of times during its life (such as in back lighted avionics instrument displays), the filaments can be too short-lived.
In accordance with the present invention, there is featured the provision of controlled current drive for the cathodes of such lamps and a concomitant enhancement in the life cycle of such cathodes. Prior art voltage driven cathodes are short lived for two main reasons, namely, (i) excessive peak power in the filament upon cold start-up due to low resistance of cold tungsten and (ii) inconsistent filament power due to contact and mounting resistance in the mechanical structure between the voltage supply and the tungsten filament.